This invention relates to power generation systems. More specifically, this invention relates to power generations systems that use steam to generate power.
Coal-fired steam boilers are currently used in conjunction with steam turbine systems for generating power, such as electricity. Referring to prior art FIG. 1, a prior art power generation system 10 has a coal-fired steam boiler 12, a steam turbine system 14, a condenser 16, and a fume cleaning system 23. A coal flow 18 and an air stream 20 is directed into the coal-fired steam boiler 12. The coal flow 18 is combusted in the boiler 12 to generate thermal energy and a boiler emission stream 22. The boiler emission stream 22 passes through the fume cleaning system 23 to produce a cleaner emission stream 25. A water flow 24 is directed through an enclosed manifold 26 in the boiler 12 and retains a portion of the thermal energy generated, thereby producing a steam flow 28. The steam flow 28 is directed through, and expanded in, the steam turbine system 14 that has a high pressure turbine 30, an intermediate pressure turbine 32, and a low pressure turbine 34, serially arranged on a shaft 36 that is connected to a generator 38. The expanding steam flow 28 causes the turbines and shaft to rotate, that in turn generates electricity via the generator 38. A fully expanded steam flow 40 exits the low pressure turbine 34 and is condensed in condenser 16 to form the water flow 24. A make-up water feed 42 augments the water flow 24 as needed. This is only a general flow chart of a power generation system and other systems may have other arrangements.
The prior art power generation system 10 that uses coal-fired boilers 12 have pollution and efficiency problems. The coal-fired boilers produce regulated emissions such as NO.sub.x, SO.sub.x, particulates, topic species, and greenhouse gas emissions. A number of attempts have been made to reduce the amount of regulated emissions from coal-fired steam boilers. Low NO.sub.x burners have been used in the boilers to reduce the NO.sub.x levels in the emissions. The fume cleaning system 23 may include scrubbers to remove the SO.sub.x and a stack glass fabric filter (baghouse) to remove the particulates. The regulated emission removal requirements are expensive to install and generally lower the overall plant efficiency. In addition, the species, green-house gases and other emissions components cannot be readily reduced with current technology. Further, the efficiency of the prior art generation systems 10 that uses coal-fired boilers 12 is limited by the energy of the steam generated. The highest typical superheat stream temperature from a boiler is about 1000.degree. F., with advanced boiler designs producing 1200.degree. F. steam. If the efficiencies were increased, then less coal would need to be burned, thus reducing the pollution emissions.
However, numerous prior art power generation systems that use coal-fired boilers exist, representing an enormous capital investment. Therefore, a need exists to generate power with higher efficiency and less pollution while retaining the capital investment of the existing power generation systems.